[toplevel] add --fail-on-bug option

Summary:
It can be useful in some situations for Infer to exit with an error code in
case it found a bug. A bug is anything Infer reports in infer-out/report.json.
This adds a flag `--fail-on-bug` to the toplevel infer script.

closes #139

infer/bin/infer

@@ -4,6 +4,7 @@ import argparse
 import imp
 import utils
 import inferlib
+import json
 import logging
 import os
 import sys
@@ -164,5 +165,16 @@ def main():
         analysis.analyze_and_report()
         analysis.save_stats()
 
+    if args.fail_on_bug:
+        bugs_filename = os.path.join(args.infer_out,
+                                     utils.JSON_REPORT_FILENAME)
+        try:
+            with open(bugs_filename) as bugs_file:
+                bugs = json.load(bugs_file)
+                if len(bugs) > 0:
+                    sys.exit(inferlib.BUG_FOUND_ERROR_CODE)
+        except OSError:
+            pass
+
 if __name__ == '__main__':
     main()

infer/bin/inferTraceBugs

@@ -21,7 +21,6 @@ import sys
 import utils
 
 BASE_INDENT = 2
-JSON_REPORT = 'report.json'
 # how many lines of context around each report
 SOURCE_CONTEXT = 2
 
@@ -249,7 +248,8 @@ class Selector(object):
 def main():
     args = base_parser.parse_args()
 
-    with open(os.path.join(args.infer_out, JSON_REPORT)) as report_file:
+    report_filename = os.path.join(args.infer_out, utils.JSON_REPORT_FILENAME)
+    with open(report_filename) as report_file:
         reports = json.load(report_file)
 
     sel = Selector(args, reports)

infer/bin/inferlib.py

@@ -47,6 +47,7 @@ ERROR = 'ERROR'
 WARNING = 'WARNING'
 INFO = 'INFO'
 
+BUG_FOUND_ERROR_CODE = 2
 
 def get_infer_version():
     try:
@@ -102,13 +103,20 @@ base_group.add_argument('-nf', '--no-filtering', action='store_true',
                         help='''Also show the results from the experimental
                         checks. Warning: some checks may contain many false
                         alarms''')
+base_group.add_argument('--fail-on-bug', action='store_true',
+                        help='''Exit with error code %d if Infer found
+                        something to report'''
+                        % BUG_FOUND_ERROR_CODE)
+
 base_group.add_argument('-l', '--llvm', action='store_true',
-                        help='Analyze C or C++ file using LLVM translation')
+                        help='''[experimental] Analyze C or C++ file using the
+                        experimental LLVM frontend''')
 
 base_group.add_argument('--log_to_stderr', action='store_true',
                         help='''When set, all logging will go to stderr instead
-                        of log file''')
-base_parser.add_argument('-v', '--version', help='Get version of the analyzer',
+                        of the log file''')
+base_parser.add_argument('-v', '--version',
+                         help='''Print the version of Infer and exit''',
                          action=VersionAction)